The javadoc for ILoggingEvent#getNanoseconds() says:

@return the number of elapsed nanoseconds since epoch

The default implementation simply returns the result of calling Instant#getNano(). However this method returns the number of nanoseconds, later along the time-line, from the start of the second - and not since _epoch._

There seems to be a mismatch between the javadoc and the default implementation provided by the interface.